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Unformatted text preview: Conditions for equilibrium Equilibrium: acceleration a = 0 Static equilibrium: Translation F = m a = 0 Rotation M = I = 0 For more than one force system, each component is not necessary zero, but each component of the summarized force is zero If a system is in equilibrium, then each of its parts is in equilibrium All components in Cartesian coordinate are zero as well based on pythagorean theorem Statically determinate and statically indeterminate system Free body diagram A draw of the body interested Free and isolated from all external structures Describes all forces and moments by proper external exerted forces Interaction between the body and its environment Help identify the forces and moments acting on individual parts of a system All know and unknown forces and moments are shown The known force and moment are indicated with direction Since each of its parts is in equilibrium, the free body diagram can be used for each one It can make fictitious cuts to isolate parts of a body in order to quantify internal force and moment that are necessary to maintain equilibrium Center of gravity determination Center of gravity Center of mass Difference of center gravity and center of mass They are almost the same for biomechanics Gravity line Center line determination figure Constrain and Reaction Force Force Active External force Reactive: unknown Constraining forces and moments acting on a body Built in structure: Hinged point: Fixed point Examples (4.2) of a free body diagram...
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